We present in this paper an original approach to the modeling of surface-channel FETs which leads to complete models valid for all operating regimes. Using a unified charge control model we obtain analytical expressions for the channel current and total terminal charges. By including short-channel effects using appropriate physically-based equations the new technique is extended to deep submicron devices. All equations have an infinite order of continuity; this is very useful in analog design, where accurate expressions of the derivatives of current and charges are needed.